1. Field of the Invention
The present invention relates to a radio frequency (RF) signal level control apparatus for a video cassette recorder (VCR), and more particularly to an automatic RF signal level control apparatus for a VCR which can keep the RF channel signals recorded on or reproduced from a video tape by channel heads in the same signal level by compensating for the level difference between the RF channel signals.
2. Description of the Prior Art
A conventional RF signal processing apparatus for a VCR is shown in FIG. 1. Referring to FIG. 1, the conventional apparatus includes pre-amplifiers 4,5 for amplifying RF channel signals reproduced from a video tape I by channel heads 2,3, respectively, a first switching section 6 for switching the RF channel signals amplified by the pre-amplifiers 4,5 in accordance with an input head switching signal H/S and outputting a switched RF signal, and an output amplifier 7 for amplifying the switched RF signal.
The conventional apparatus is also provided with an automatic gain control (AGC) level detector 8 for detecting an AGC signal level of the RF signal outputted from the output amplifier 7, a level generator 9 for generating a predetermined level signal level for AGC, and a second switching section 10 for selecting one of the output signals of the AGC level detector 8 and of the level generator 9 in accordance with an external input control signal CTL, and providing the selected signal to the output amplifier 7 as a gain control signal thereof.
The operation of the conventional apparatus constructed as described above will be explained with reference to FIG. 1 and FIGS. 2A to 2D.
The RF channel signals recorded on the video tape 1 are read out by the respective channel heads 2,3 and then amplified by the respective pre-amplifiers 4,5 to be inputted into the first switching section 6.
FIG. 2A represents one RF channel signal reproduced by the head 2 and FIG. 2B represents the other RF channel signal reproduced by the head 3.
The RF channel signals reproduced and inputted to the first switching section 6 as described above, are switched in conformity with the input timing of the respective RF channel signals according to the input head switching signal H/S as shown in FIG. 2C. As a result of the switching, the RF signal outputted from the first switching section 6 is shown in FIG. 2D. The switched RF signal is then amplified by the output amplifier 7 to be outputted through a terminal OUT for the following signal processing.
Meanwhile, the AGC level detector 8 detects the level of the output RF signal and the detected level signal is selectively fed back to the output amplifier 7 via the second switching section 10 as an AGC signal of the output amplifier 7, thereby stably controlling the gain of the output amplifier 7. That is, the second switching section 10 is switch-controlled according to the external control signal CTL and selects one of the output signals of the AGC level detector 8 and of the level generator 9. The selected signal is then fed back as the AGO signal of the output amplifier 7.
However, the problem in the above-described conventional RF signal processing apparatus has is that the RF signal finally reproduced and outputted has a level difference between the respective channels, as shown in FIG. 2D, in cases where the levels of the RF channel signals reproduced by the respective heads 2, 3 are different from each other, as shown in FIG. 2D, due to mechanical tolerance of the heads, recording error, electrical characteristics of the signal reproducing system, etc. Such problems may be also faced in recording the RF signal on the video tape. If the level difference between the channel signals occurs in any case, deteriorations of picture quality and of sound quality may also be generated.